A Multiscale Transient Modeling Approach for Predicting the Solidification Structure in VAR-Processed Alloy 718 Ingots

This paper describes the development and validation of a comprehensive multiscale modeling approach capable of predicting at the mesoscopic scale level the ingot solidification structure and solidification-related defects commonly occurring during the vacuum arc remelting (VAR) process. The approach consists of a coupling between a fully transient macroscopic code and a mesoscopic solidification structure code. The predictions from the multiscale model, including grain morphology and size and columnar-to-equiaxed transition, were validated against experimental measurements for a 20-inch (508 mm) diameter VAR alloy 718 ingots. The validated model was then used to investigate the effects of melting rate and ingot diameter on the solidification structure of VAR processed 718 ingots.     

气氛保护电渣重熔铍铜合金QBe2.0的冶金质量研究

QBe2.0合金是用量最大的航空航天铍铜合金,分别采用真空感应熔炼(Vacuum Induction Melting,VIM)+半连续铸造(Semicontinuous casting)和真空感应熔炼(VIM)+气氛保护电渣重熔(Protected Electro Slag Remelting,P-ESR)两种不同工艺生产QBe2.0合金,通过超声探伤和断口检测分别对两种工艺生产的铸锭和后续锻造棒材的冶金材料质量进行对比实验研究.结果表明,与常规工艺相比,气氛保护电渣重熔过程具有熔池过热度低,熔池浅,过程一致性好和高度方向组织均匀等优点,生产的QBe2.0合金铸锭中易氧化元素Be没有明显的烧损,氧含量[O]由常规的0.01233％(质量分数)降低到了0.00238％,金相组织得到了明显改善,组织更均匀更加细小,尤其是锻造棒材中的β相较少,且呈点状分布,锻造加工后探伤和断口检测结果都达到了标准要求,从根本上解决了长期以来国内采用半连续铸造方法制备棒材在断口和探伤方面难于达到质量要求的问题.     

LB733合金熔铸工艺的研究

本文介绍了LB733合金的熔铸工艺特性,重点分析了其铸锭裂纹的成因、形态、性质及预防方法。     

电子束冷床炉单次熔炼钛合金铸锭研究进展

电子束冷床炉单次熔炼钛合金技术是一种先进的钛合金铸锭低成本制备技术,引起了国际钛工业越来越多的关注。本文对电子束冷床炉单次熔炼钛合金技术从成分及组织控制、实际生产情况及电子束冷床炉单次熔炼直接轧制板材的性能评价等方面进行综合评述。     

GH4169合金VIM+PESR+VAR三联冶炼工艺及其冶金质量

介绍了GH4169合金508锭的VIM+PESR+VAR三联工艺及其冶金效果和实物质量。结果表明,较之VIM+VAR双联工艺浇铸的电极,三联工艺PESR制作的电极由于没有缩孔、组织致密、纯洁度高,VAR冶炼的工艺稳定性显著提高,且VAR过程中掉块的几率大幅度降低,因而,宏观缺陷的出现率大幅度下降。同时由于PESR良好的脱硫、去氧作用,三联工艺成品锭硫、氧含量显著下降,热塑性也明显改善。此外,纯洁度的提高,势必导致氮化物、碳化物形成核心减少,加之工艺参数稳定性的提高,三联工艺成品材中碳化物分布的均匀性也有所改善。     

Purification of an industrial aluminum alloy by melt stirring during ohno continuous casting process

With the purpose of upgrading the purity of a dilute industrial aluminum alloy during Ohno Continuous Casting (OCC) process through the use of forced melt stirring; the critical stirring intensity required under a casting speed of 2 mm/min was numerically determined. The determined critical stirring intensity induces convective velocity magnitudes into the melt which are effective in transporting solutes from the solute boundary layer into the bulk melt. It was found that, with adequate melt stirring, production of substantially long and high purity ingots during OCC is possible before their purity diminishes to lower than the initial alloy purity.     

Observations of melt rate as a function of arc power,CO pressure,and electrode gap during vacuum consumable arc remelting of Inconel 718

Statistically designed experiments were conducted at two different production melt shops to evaluate the influence of arc power, CO pressure, and electrode gap on melt rate. Approximately 11,000 kg of Inconel 718 alloy 0.4 m diameter electrodes were vacuum consumable arc remelted into 0.5 m diameter ingots. Analysis of the experimental results revealed that melting efficiency (melting rate/kW) was maximized when CO pressure and electrode gap were held at low levels. Under these conditions, the heat distribution (created by the vacuum arc) on the electrode tip and the molten pool exhibited macro uniformity. Increased CO pressure and/or electrode gap depressed the melt rate, and at 13.3 Pa (100 microns) and a 0.050 m electrode gap, this depression exceeds 46 pct. Increasing these parameters also changed the arc behavior to that of a constricted arc with a highly localized heat input. It is hypothesized that the change from the usual diffuse arc to this constricted arc results in intense Lorentz pumping in a localized region of the molten pool atop the ingot causing fluid flow transients. These transients could, in turn, create solidification defects.     

Solidification of a Vacuum Arc-Remelted Zirconium Ingot

As the quality of vacuum arc-remelted (VAR) zirconium ingots is directly linked to their chemical homogeneity and their metallurgical structure after solidification, it is important to predictively relate these factors to the operating conditions. Therefore, a detailed modeling study of the solidification process during VAR has been undertaken. To this purpose, the numerical macromodel SOLAR has been used. Assuming axisymmetrical geometry, this model is based on the solution of the coupled transient heat, momentum, and solute transport equations, under turbulent flow conditions during the remelting, hot-topping, and cooling of a cylindrical ingot. The actual operating parameters are defined as inputs for the model. Each of them, mainly the melting current sequence, melting rate sequence, and stirring parameters (current and period), is allowed to vary with time. Solidification mechanisms recently implemented in the model include a full coupling between energy and solute transport in the mushy zone. This modeling can be applied to actual multicomponent alloys. In this article, the macrosegregation induced by solidification in a zirconium alloy ingot is investigated. In order to validate the model results, a full-scale homogeneous Zy4 electrode has been remelted, and the resulted ingot has been analyzed. The model results show a general good agreement with the chemistry analyses, as soon as thermosolutal convection is accounted for to simulate accurately the interdendritic fluid flow in the central part of the ingot.     

轿车同步器齿环用锰黄铜HMn59—2—1—0.5熔炼工艺探讨

对低频有芯感应电炉熔炼ＨＭｎ５９－２－１－０．５复杂黄铜工艺进行了探讨。熔炼过程中,锌、铝、锰是易烧损元素,在确定配料比和出炉控制范围时,要予以考虑,在旧料回炉时应按一定比例补偿;难熔元素硅,锰应以溶解的方式加入,铁以中间合金加入较好。合理的工艺条件可以保证为铸造产品提供均匀合格的合金熔体。     

固定自耗电极充填法电渣熔铸铸锭底部成形性研究北大核心CSCD

用固定自耗电极充填法电渣熔铸了横断断面为400 mm×60 mm的板形铸锭,用实验与数值模拟方法研究了铸锭底部成形性。结果表明:固定自耗电极充填法电渣熔铸板形铸锭时熔铸过程稳定、可控,表面质量良好;熔铸铸锭时,固定电极底部斜度有利于固定自耗电极平稳地进入电渣,其斜度的大小直接影响铸锭底部的成形性,斜度越大铸锭底部成形性越差。铸锭底部形状数值模拟结果与实验结果基本吻合。     

坩埚冷却系统改造对中间合金熔炼的影响

以Zr-Sn—Fe—Cr—Ni合金为研究对象,通过2次非自耗真空电弧熔炼制备出中间合金,对熔炼中间合金时所采用的坩埚的冷却系统进行了改造,对比了改造前后中间合金的熔炼过程,并采用OM、EDS研究了中间合金的组织及化学成分,冉以添加中间合金扣方式压制电极,利用真空自耗电极熔炼方式制备出吨级锆合金铸锭,并对成品铸锭的成分进行跟踪。结果表明：在坩埚中加入导流槽后,中间合金的熔炼效率得到了提高,熔炼时难脱模现象大大缓解;采用加导流槽后的坩埚经过2次熔炼可以制备出成分均匀的中间合金,合金组织由柱状品和树枝晶组成,与未加导流槽时所熔炼的合金相比,组织及成分更加均匀;采用冷却系统改造后的坩埚熔炼的中间合金可以制备出成分均匀的工业规模级锆合会铸绽。     

Numerical simulation of dendrite white spot formation during vacuum arc remelting of INCONEL718

White spot is the term for a particulate dispersion lean in niobium found in vacuum arc remelted (VAR) ingots of niobium containing nickel-based superalloys, such as INCONEL718, that can be detrimental to the mechanical properties. While spot can result from exogenous fragments that fall into the VAR melt pool and remain incompletely melted. In this study, white spot formed when dendrite clusters fall-in from the shrinkage pipe of vacuum induction melted (VIM) electrodes is considered by simulations. The motion and dissolution of the dendrite cluster particles were simulated in the framework of a macroscopic heat and fluid flow model of the VAR process. Two scales of heat and mass transfer are considered within the cluster: interdendritic solute diffusion within particles and the thermal interaction between the particle and the bulk convective melt. The dissolution behavior of dendrite cluster fall-in was investigated for a range of initial particle conditions including solid fraction, Nb content, drop height, and initial temperature. The operational window where the exogenous particles completely dissolve was determined as a function of cluster size, density, and location. It was found that particles smaller than 3 mm are completely dissolved under all conditions simulated in this study. All factors studied demonstrated significant influence on particle dissolution. Particles with a solid fraction less than 0.5, a Nb content greater than 4 pct, or an initial temperature greater than 1400 K are likely to be dissolved immediately after entering the melt pool. Drop height and initial density had the greatest effect on particle dissolution.     

GH901合金采用电渣重熔工艺时Ti含量的控制研究

主要讨论了GH901合金采用电渣重熔工艺时，不同Ti含量的母材在电渣重熔过程中经过脱氧荆添加量的调整冶炼出合格的电渣锭，进而得出该合金采用电渣重熔工艺时根据母材Ti含量的不同，添加合理的脱氧剂量。     

大直径铝锭热顶铸造中超声施振深度的细晶机制

在直径为650 mm的铝合金热顶半连续铸造过程中施加双源超声振动系统, 研究3种超声辐射杆浸入深度对铸锭宏观凝固组织的影响.基于铝合金铸锭凝固组织形貌的检测结果以及ANSYS等有限元软件对铸造过程中声场的仿真结果, 深入探讨了超声辐射杆在不同的施振深度下对铝合金铸锭凝固组织细化机制的影响.结果表明: 随着超声辐射杆施振深度的增加, 铸锭截面组织整体进一步细化, 晶粒形状由发达的枝晶变为等轴枝晶; 由于超声辐射杆端面以及柱面存在几个固定位置处振动波峰, 在铝熔体中不同的超声施振深度下存在不同的超声空化范围, 进而导致凝固组织的细化机制也不同.      

真空电渣重熔炉发展前景的探讨

真空电渣重熔炉是在真空电弧重熔炉和气体保护电渣炉的基础上发展起来的一种冶炼高性能合金的特殊真空重熔冶金装备。真空电渣重熔炉冶炼的钢种和合金有优质合金钢,高温合金,精密合金,耐蚀合金,铝、钛、银等合金。介绍了真空电渣重熔炉的工作原理,冶金特点,比较了真空电弧重熔、普通电渣重熔和真空电渣重熔的钢材的冶炼成本、冶金质量和性能,并讨论了真空电渣重熔炉的应用前景。     

Fatigue crack growth rates and fracture toughness of rapidly solidified Al-8.5 pct Fe-1.2 pct V-1.7 pct Si alloys

The room-temperature fatigue crack growth rates (FCGR) and fracture toughness were evaluated for different crack plane orientations of an Al-8.5 Pct Fe-1.2 Pct V-1.7 Pct Si alloy produced by planar flow casting (PFC) and atomized melt deposition (AMD) processes. For the alloy produced by the PFC process, properties were determined in six different orientations, including the short transverse directions S-T and S-L. Diffusion bonding and adhesive bonding methods were used to prepare specimens for determining FCGR and fracture toughness in the short transverse direction. Interparticle boundaries control fracture properties in the alloy produced by PFC. Fracture toughness of the PFC alloy varies from 13.4 MPa√m to 30.8 MPa√m, depending on the orientation of the crack plane relative to the interparticle boundaries. Fatigue crack growth resistance and fracture toughness are greater in the L-T, L-S, and T-S directions than in the T-L, S-T, and S-L orientations. The alloy produced by AMD does not exhibit anisotropy in fracture toughness and fatigue crack growth resistance in the as-deposited condition or in the extruded condition. The fracture toughness varies from 17.2 MPa√m to 18.5 MPa√m for the as-deposited condition and from 19.8 MPa√m to 21.0 MPa√m for the extruded condition. Fracture properties are controlled by intrinsic factors in the alloy produced by AMD. Fatigue crack growth rates of the AMD alloy are comparable to those of the PFC alloy in the L-T orientation. The crack propagation modes were studied by optical metallographic examination of crack-microstructure interactions and scanning electron microscopy of the fracture surfaces.     

Method Developed for Quantitative Analysis of Inclusions in Solidified Aluminum Ingots

A deep-etching method was used to determine inclusions in solidified direct chill cast aluminum ingots. The technique was developed to allow easy quantification of the amount and size distribution of inclusions over billet lengths and cross sections. A pressure filtration (Prefil) test also was used to verify molten alloy cleanliness during casting, and the results of these measurements then were compared. The amount and distribution of nonmetallic inclusions were analyzed, as determined using a NaOH deep-etching method over billet lengths and cross sections. A higher inclusion count was observed at both billet ends, with more inclusions located nearer the billet section centerline. Furthermore, the inclusion density in the radial direction at every distance along the billet length was distributed inhomogeneously. Differences were observed between Prefil samples taken at different casting stages. The Prefil curves and metallographic analysis of Prefil residue obtained from melt samples, at an early casting stage or before degassing, indicate more oxides than in a melt sample taken under steady-state casting conditions. A reasonable correlation was established between the number of inclusions in the molten alloy (measured using Prefil and LiMCA) and the etch pits on deep-etched surfaces of billet cross sections.     

基于数值模拟的镍基高温合金电渣重熔工艺优化

利用MeltFlow软件对镍基高温合金电渣重熔过程进行数值模拟计算,探究了电渣重熔过程中温度场、流场、熔池形貌及微观组织的分布特点,通过工业试验验证模拟的准确性,定量分析熔速对熔炼过程的影响规律,提出了一种改善铸锭凝固质量的工艺优化方法.结果 表明,渣池内的温度相对较高且分布均匀,熔池形貌近似"V"型.铸锭一次枝晶间距...     

Ti-51111S合金熔炼工艺研究

通过对Ti-51111S合金铸锭生产工艺的研究,分析中间合金加入、电极制备方式及熔炼参数对铸锭生产及化学成分均匀性的影响,探索出合理的Ti-51111S合金铸锭生产工艺。采用该工艺生产的Ti-51111S合金铸锭成分均匀,冶金质量良好,符合有关技术条件要求,可以满足民用钛材使用要求。     

Effects of low-frequency electromagnetic field on the surface quality of 7050 aluminum alloy ingots during the hot-top casting process

To improve the quality of 7050 aluminum alloy ingots, low-frequency electromagnetic (LFE) field was applied during the conventional hot-top casting process. Macrostructures and microstructures of the ingots by the conventional and LFE hot-top casting processes were studied. The experimental results show that when the LFE field is turn off during the hot-top casting process, cold folding appears, and the as-cast structure becomes very coarse. Additionally, the thickness of the shell zone is much thinner during the low-frequency electromagnetic hot-top casting process than that during the conventional hot-top casting process. Some reasons for low-frequency electromagnetic field improving the surface quality, refining the structure of the ingot, and minimizing the thickness of the shell zone have been studied.